Method and apparatus for slush molding articles of footwear

ABSTRACT

In a slush molding process for producing a boot or shoe from a plastisol, a mold in the shape of the article of footwear is filled with liquid plastisol, the mold is heated to form a skin, the mold is tilted to pour out excess plastisol, and, after filling the heel cavity of the mold, the skin and heel filler are cured or hardened, and the skin is removed from the mold and trimmed for further processing. Instead of filling the heel cavities of the molds with a specially formulated heel filling composition, the skin trimmings, which were previously discarded as waste, can be ground, if necessary, mixed with additional stabilizer and injected into the heel cavities using an injection unit. With the molds travelling along a straight line path of travel, it is necessary to cause the nozzle end of the injection unit to move in synchronism with the molds. For such purpose, the injection unit is mounted on a shaft which is rotated by a drive train connected to the conveyor chain carrying the molds or the drive of the conveyor chair. In order to cause the nozzle of the injection unit to follow the same straight line path of travel as the molds, the shaft and injection unit are mounted on a carriage slidable towards and away from the molds, and a cam device controls sliding of the injection unit so that the nozzle is maintained in position over a mold during each heel filling operation. By utilizing the waste material instead of a specially formulated heel filling material, the cost of producing the heel and consequently the cost of the article of footwear as a whole is substantially reduced.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method and apparatus for filling a mold, andin particular to a method and apparatus for filling the heel cavity of amold used in a slush molding machine for manufacturing articles offootwear.

2. Description of the Prior Art

The A. Cervinka Canadian Pat. Nos. 592,262 and 594,464, issued Feb. 9,1960 and Mar. 15, 1960, respectively, describe the production ofcalf-length boots using a slush molding process in which a mold in theshape of the boot is filled with a plastisol, e.g. polyvinyl chloride,the mold is heated to cause the plastisol to gel and form a skin, excessplastisol is poured from the mold, and the mold is again heated to curethe plastisol.

As mentioned in applicant's Canadian Pat. No. 995,866, issued Aug. 31,1976, when molding winter boots or the like with large heels,difficulties may be experienced in filling the heel cavity. It isnecessary to fill the heel cavity exactly; otherwise, the finishedproduct is uncomfortable to the point of being useless. Canadian Pat.No. 995,866 describes an automatic heel filling device which includes adispenser mounted on the molding machine and capable of travelling withthe mold for filling the heel cavity. The device utilizes aheat-hardenable plastisol, which fills the heel cavity and is cured withthe skin.

It has been found that use of the slush molding method and machinedescribed above with a heat-hardenable plastisol results in a largequantity of waste. Following formation of the skin, the top of the skinis removed by cutting to form a straight top edge of the boot. Theexcess skin is discarded as waste, and the skin is further processed,i.e. provided with a liner and otherwise finished to provide a boot.With a continuous slush molding process, large quantities ofthermoplastic material are discarded as waste. Moreover, it is necessaryto provide a separate plastisol for filling the heel.

Accordingly, a method and apparatus which utilize such wastethermoplastic material have obvious advantages. It has been found thatin order to re-use the waste thermoplastic material, it must be madeliquid and remain in liquid form until it is dispensed into the heelcavity of the mold. Liquification is achieved by grinding the wastethermoplastic material, possibly mixing it with a stabilizer and heatingthe resulting mixture to form a flowable thermoplastic mass. Once themixture has been heated, it must remain heated until it is dispensedinto the mold. Thus, the heel filling device described in Canadian Pat.No. 995,866 cannot be used to fill heel cavities with the thermoplasticmass, since the mixture would cool during passage to the mold.

The object of the present invention is to provide a method and apparatuswhich permit the use of waste plastisol for filling the heel cavity in aslush molding process.

SUMMARY OF THE INVENTION

Accordingly, the present invention relates to a method of slush moldingarticles of footwear including heel and upper portions, including thesteps of continuously conveying a plurality of molds along a path oftravel; filling each mold with a plastisol; heating said molds to cure aportion of said plastisol, thereby forming a plastisol skin on theinterior of the mold; discharging excess plastisol from the mold whileleaving the skin in the mold; filling the heel portion of said skin witha plastic material; and curing the heel portion, the improvementcomprising using a thermoplastic material for filling the heel portionof said skin.

More specifically, recycled, waste thermoplastic material such as thatobtained by trimming excess portions of the skin formed during the slushmolding process is used to form the heel of the article of footwear. Byrecycled is meant waste material which is treated to make it usable inthe process of the present invention, and the term "thermoplastic" isintended to mean a plastic which is hardened by cooling.

A typical composition for use in the slush molding process to form theskin of a shoe or boot includes a resin such as polyvinyl chloride, aplasticizer such as dialkyl phthalate, a stabilizer such as abarium/cadmium/zinc complex and colour pigments. In some cases, it maybe possible to re-grind waste skin composition and use it to fill heelcavities. However, when using such re-ground skin compositions, thereare the dangers of deformation in large heel cavities and decompositiondue to heating. Accordingly, it may be necessary to add additionalresin, plasticizer and/or stabilizer to the re-ground skin composition.

The present invention also relates to an apparatus for filling heelcavities of footwear molds continuously moving along a rectilinear pathof travel comprising a stationary frame adjacent to said path of travel;a carriage slidably mounted on said frame for movement towards and awayfrom said path of travel; an injection unit rotatably mounted on saidcarriage for movement with the carriage towards and away from said pathof travel; nozzle means on the discharge end of said injection unit fordispensing thermoplastic material into the heel cavity of a mold; firstdrive means for moving said injection unit in synchronism with a mold inthe direction of said path of travel; and cam means engageable by saidinjection unit for causing the nozzle to follow the rectilinear path oftravel of said mold.

Because the barrel of the injection unit is heated for melting thethermoplastic material, the injection unit must be in continuous use,i.e. a shot of thermoplastic material must be discharged from the unitat frequent intervals. Otherwise, the injectable thermoplastic would beoverheated and become scorched and degraded. The molds are normallyspaced equidistant apart on carriers connected to a continuously movingchain. However, there are occasions when there is no mold on a moldcarrier, and, on such occasions, the injection unit is automaticallypurged, the shot of thermoplastic material being dispensed into a wastereceptacle located beneath the nozzle of the unit. The nozzle of theinjection unit can either move in synchronism with a mold or move awayfrom the path of travel of the molds for manual purging or servicing, orremain stationary and be purged when no mold is present.

Using the method and apparatus of the present invention in theproduction of articles of footwear with large heels, there is asubstantial reduction in production time. Since the heel material isthermoplastic, it must be cooled to harden. Thus, the shorter the timein the heaters for curing the plastisol of the skin, the quicker thehardening of the heel. With a plastisol heel, a relatively lengthyheating or curing time is required, while the thermoplastic material canbe passed through the heaters quickly. Because no heat is required forcuring the heel, the use of a thermoplastic material results in asubstantial saving of energy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view of a slush molding machine incorporatingthe apparatus of the present invention;

FIG. 2 is a perspective view of the apparatus in accordance with thepresent invention in position adjacent to a molding machine;

FIG. 3 is a longitudinal sectional view of a portion of a drivemechanism for imparting rotary motion to the injection unit;

FIG. 4 is a cross-sectional view taken generally along line IV--IV ofFIG. 3;

FIG. 5 is an elevation view of the remainder of the drive mechanism ofFIG. 3;

FIG. 6 is an elevation view of an alternate form of drive mechanism forimparting rotary motion to the injection unit;

FIG. 7 is a cross-sectional view of the drive mechanism of FIG. 6 takengenerally along line VII--VII of FIG. 6;

FIG. 8 is a perspective view of a cam device for causing the nozzle ofthe injection unit to follow a rectilinear path of travel;

FIG. 9 is a partly sectioned front view of the cam device of FIG. 8;

FIG. 10 is a cross-sectional view of the cam device of FIGS. 8 and 9;

FIGS. 11 and 12 are schematic elevation views of roller and pin elementsof the cam device of FIGS. 8 and 10;

FIG. 13 is a schematic plan view of the elements of FIGS. 11 and 12; and

FIG. 14 is a partly sectioned, elevation view of a nozzle device used onthe injection unit of FIG. 2.

DESCRIPTION OF PREFERRED EMBODIMENT APPARATUS

With reference to FIG. 1, the apparatus of the present invention isintended for use with a slush molding machine including a conveyor inthe form of a chain 1 carrying a plurality of carriers 2 (one shown inFIG. 2) spaced equidistant apart along the length of the chain. Thechain 1 and carriers 2 normally follow a path of travel which isrectangular with semi-circular ends. Each of the carriers 2 supports amold 3 in the shape of a boot or shoe. In the slush molding process, themolds 3 are loaded onto the conveyor 1 at loading station 4, and eachmold 3 is filled with plastisol such as polyvinyl chloride by a moldfilling device 5. The plastisol is pumped from tanks 6 by a filling pump7 and a pressure tank 8 to the filling device 5. A vacuum pump 9 isprovided for deaerating the tanks 6 to prevent the formation of bubblesin the plastisol.

The filled molds 3 are carried by the conveyor 1 through a first bank ofovens 10 for partially curing the plastisol to form a skin on the innersurface of the molds. Excess plastisol is discharged from the molds bytilting them at a drainage location 11 and returned to the tanks 6 forre-use. The molds 3 with the skins therein are passed through gellingovens 12 past a pneumatic limit valve 13 and a shot size selector sensor14 described hereinafter, to a heel filling apparatus 15 in accordancewith the present invention and a photosensor 16 for detecting thepresence of a mold 3. After filling of the heel cavity of the skin ineach mold 3, the mold is conveyed through additional ovens 17 and 18 forcuring the skin and sole thereof, respectively. Finally, the molds 3pass through a cooling device 19 to an unloading station 20. Theconveyor 1 is driven by a conveyor drive 21. At the unloading station20, the skin is removed from the mold 3 for further processing,including trimming of excess plastisol. The excess plastisol is ground,if necessary, recycled and used in the heel filling apparatus 15 forfilling heel cavities of molds.

Referring now to FIGS. 2 to 5, the apparatus of the present inventionincludes a fixed rectangular frame generally indicated at 22 mounted onthe floor beside the conveyor 1. The frame 22 includes legs 23, sides24, ends 25, longitudinal braces 26 and cross bars 27 near the bottomsof the legs. A cylindrical track 28 is mounted in corner brackets 29 oneach side of the frame 22 for slidably supporting a carriage 30 formovement towards and away from the molding machine. The carriage 30 isin the form of a pair of rectangular blocks 31 joined together at theirends by plates 32, with arm 33 extending outwardly from each outsidecorner of the blocks. The tracks 28 extend through bushings mounted inapertures in the arms 33.

An injection unit 34 is rotatably supported on the carriage 30 by meansof a large diameter, cylindrical shaft 35. The injection unit 34 is aconventional element with a cylinder 36 at the rear end thereof fordriving a ram (not shown) which discharges plastic material from ahopper 37 through a heated cylinder 38 and a nozzle device generallyindicated at 39 into the heel cavity of a mold 3.

With reference to FIG. 3, the shaft 35 is mounted in roller bearings 40in a sleeve 41 in the centre of the carriage 30, the bearings 40 and thesleeve 41 being retained on the shaft 35 by a nut 42 on a threadedcentral portion 43 of the shaft. The injection unit 34 is mounted on arectangular plate 44 and centered on the shaft 35 by a centering pin 45extending upwardly from the shaft through the plate 44. A cap 46 iswelded to the plate 44 and extends downwardly around the sleeve 41,being spaced therefrom by bushings 47. The bottom end of the shaft 35 isstepped, i.e. has reduced diameter lower portions, and is rotatablymounted in roller bearings 48 and 49 in a casing 50 connected to thebottom of the carriage 30.

The shaft 35, the cap 46, the plate 44 and the injection unit 34 arerotated by a gear quadrant 51 (FIGS. 3 and 4) secured on the bottom endof the shaft 35 in the casing 50. The gear quadrant 51 is keyed on theshaft 35 by a rectangular key 52. The teeth 53 (FIG. 4) of the gearquadrant 51 engage a pinion 54 securely mounted on a shaft 55 by asquare key 56 in the casing 50. The shaft 55 is rotatably mounted inroller bearings 57 in the top and bottom of the casing 50, and extendsdownwardly out of the casing.

In order to rotate the injection unit 34 in synchronism with a mold 3,the shaft 55 is driven by a drive train connected directly to the chain1 for conveying mold carries 2 and molds 3. The drive train (FIGS. 2 and5) includes a sprocket 58 rotatably mounted on a plate 59 on the moldingmachine frame in constant engagement with the chain 1. The sprocket 58is mounted on a shaft 60 which also carries a gear 61 for driving a gear62, which is also rotatably mounted on the plate 60. The gear 62 ismounted on the top end of a shaft 63 which is connected by universaljoints 64 and a shaft 65 to a corner joint 66. The joint 66 is connectedby universal joints 67, and shafts 68 and 69 to a clutch 70. The shaftis suspended from a plate 71 attached to the front cross bar 27 of theframe 22 by brackets 72.

The clutch 70 is connected to a reduction gear 73, which is suspendedfrom a plate 74 mounted on the front cross bar 27 of the frame 22 andconnected to the frame side 24 by a diagonal brace 75 (FIG. 2). Thereduction gear 73 is coupled to a shaft 76 extending upwardly from theplate 74 by a universal joint 77. The top end of the shaft 76 is fixedin a sleeve 78. A shaft 79 is slidably mounted in the top end of thesleeve 78 and is connected to the bottom end of the shaft 55 by auniversal joint 80.

With reference to FIGS. 6 and 7, an alternate form of drive mechanismfor imparting rotary motion to the injection unit 34 in synchronism witheach mold 3 will now be described. Since the chain 1 may slip, it ispreferable to connect the drive mechanism for the injection unit 34 to amain take up shaft 81 of the chain 1. The shaft 81 is at one end 82(FIG. 1) of the molding machine for supporting a sprocket 83, the shaft81 and sprocket 83 being freely rotatable. The chain 1 passes around thesprocket 83 at the end 82 of the molding machine opposite the conveyordrive 21.

Thus, the preferred drive train for rotating the injection unit 34includes a reduced diameter bottom portion 84 of the shaft 81 (FIGS. 6and 7), which is connected to a torque limiting overriding clutch 85followed by a sprocket 86 mounted in a bearing 87. The bearing 87 ismounted on a bracket 88 connected to a part 89 of the molding machineframe. The sprocket 86 is connected to a sprocket 90 by a chain 91. Thechain 91 is tensioned by a sprocket 92 mounted on the outer end of anarm 93. The inner end of the arm 93 is formed by a sleeve 94 pivotallymounted on a cross-bar 95 connected to uprights 96 of the moldingmachine frame. One end of a spring 97 is pivotally connected to theouter end of the arm 93 by a sleeve 98, and the other end of the springis pivotally connected to a pin 99 in a block 100. The block 100 isslidably mounted in a slide 101 extending along the cross-bar 95perpendicular to the chain 91 for adjusting the length of the spring 97,and thus varying the tensioning pressure of the sprocket 92 on the chain91.

The sprocket 90 is fixedly mounted on the top end of a shaft 102 in abearing 103. A gear 104 is also mounted on the shaft 102 in permanentengagement with a gear 105 mounted on the top end of a shaft 106extending downwardly through a bearing 107 and a plate 108, whichsupports both of the bearings 103 and 107. A sprocket 109 mounted on thebottom end of the shaft 106 is connected by a roller chain 110 andsprocket 111 to the corner joint 66 (FIG. 2). The chain 110 is tensionedby a sprocket 112 rotatably mounted on a stub axle 113. The axle 113 ismounted on the outer end of an arm 114, which is pivotally mounted on across-bar 115. The arm 114 is fixed in one position, but can be rotatedto adjust the tension on the chain 110. The remainder of the drivemechanism for imparting rotary motion to the injection unit 34 is thesame as illustrated in FIGS. 3 to 5 and described hereinbefore.

Thus, with either form of drive mechanism linear motion of the chain 1,carriers 2 and molds 3 is translated into rotary motion of the injectionunit 34 and the shaft 35, rotation of the injection unit 34 being inunison with movement of the molds 3. When the clutch 70 is disengaged,the shaft 35 and the injection unit 34 are returned to the rest positionby a pneumatic cylinder 116. The cylinder 116 is pivotally mounted by aclevis 117 on a frame 118 (FIG. 2) extending upwardly from the rear endof the carriage 30. A piston rod 119 extends from the front end of thecylinder 116 to a generally triangular arm 120 extending outwardly fromthe cap 46 on one side of the shaft 35. The piston rod 119 is pivotallyconnected to the bifurcated outer end of the arm 120 by a clevis 121.

The frame 118 also supports a shock absorber 122, which is engaged by anarm 123 extending downwardly from the plate 44 when the injection unit34 is returned to the rest position by the cylinder 116. An additionalcylinder 124 (one shown) is provided on each side 24 of the frame 22 formoving the carriage 30 and the injection unit 34 away from the moldingmachine for manual purging or servicing. A piston rod 125 extendingrearwardly from each cylinder 124 is secured to a rear arm 33 of thecarriage 30 for moving the carriage back and forth along the tracks 28.

With the above-described arrangement of elements, the nozzle device 39on the end of the injection unit 34 would follow an arcuate path oftravel, while the molds 3 follow a rectilinear path of travel parallelto the chain 1. In order to cause the nozzle device 39 to follow thesame rectilinear path of travel as the molds 3, a cam device generallyindicated at 126 (FIGS. 2 and 8 to 13) is provided at the front end ofthe plate 44 carrying the injection unit 34.

The cam device 126 includes a base plate 127 mounted on the brackets 29at the front end of the frame 22. The base plate 127 supports a verticalfront plate 128 and rear posts 129 with tracks in the form of rods 130extending therebetween. A carriage 131 is slidably supported on the rods130. The carriage 131 is fixed in one position, which can be changed bymeans of an adjustment screw 132 extending through the front plate 128and threaded into a block 133 (FIG. 10) extending downwardly from thefront end of the carriage 131. The outer end of the screw 132 isprovided with a handle 134, and the inner end with a stop 135.

Top plates 136 and 137 on the carriage 131 with opposed arcuate surfacesdefine a cam track in the form of an arcuate cam groove 138 ofrectangular cross-sectional configuration. A cam follower defined by apin 139 with a roller 140 on the bottom end thereof extends downwardlyinto the groove 138 through an opening 141 in the plate 44 carrying theinjection unit 34. During use, the roller 140 rides in the groove 138while the nozzle is advancing with a mold 3, i.e. during filling of theheel cavity.

In order to retract the injection unit 34 for manual purging or shutdown, the roller 140 is raised so that it is completely free of thegroove 138. For such purpose, the pin 139 extends upwardly through arectangular parallelepipedic block 142. Bushings 143 are provided on thepin 139 so that the pin can slide in the block 142 and in an invertedU-shaped frame 144, which is mounted on the plate 44 and surrounds thetop and sides of the block 142. The frame 144 has an opening in the topfor the pin 139. The block 142 is provided with a longitudinallyextending, vertical slot 145 in its top for the pin 139, and with aninclined slot 146 in each of its sides for arms 147 extending outwardlyfrom each side of the pin, perpendicular thereto. Rollers 148 on thearms 147 facilitate movement of the arms in the slot 146.

A cylinder 149 is mounted on a bracket 150 on the plate 44. A piston rod151 extends outwardly from the cylinder 149 to one end of the block 142.When the piston rod 151 is extended (FIGS. 8, 9 and 12), the pin 139 androller 140 are in their lowermost position with the roller 140 in thecam groove 138, and, when the piston rod 151 is retracted (FIG. 11), thearms 147 ride up the inclined slots 146, moving the roller 140 upwardlywith the pin 139 out of the cam groove 138. Thus, the injection unit 34and the plate 44 are released from the cam device 126, and are free tofollow an arcuate path of travel when they rotate with the shaft 35.

An injection unit of the type normally used with the apparatus of thepresent invention is an off the shelf item, with a nozzle at thedischarge end aligned with the longitudinal axis of the casing of theinjection unit. In the present case, the plastic material is not beinginjected horizontally directly into a mold, but must descend at a rightangle to the longitudinal axis of the injection unit. Accordingly, thenozzle device 39 provided on the front end of the injection unit 34 hasbeen designed specifically for the apparatus of the present invention.

Referring to FIG. 14, the nozzle device 39 includes a pneumatic cylinder152 mounted on a bracket 153 (FIGS. 2 and 14) at the front end of theinjection unit 34). A casing 154 is mounted between downwardly extendingarms 155 of the bracket 153. A threaded piston rod 156 extendsdownwardly from the cylinder 152 for receiving a cup-shaped coupler 157,which connects the piston rod 156 to a plunger 158. The coupler 157 hasa closed bottom end with a slot for receiving a reduced diameter portion159 of the plunger 158. An inlet duct 160 is provided in one side of thecasing 154 near the bottom end thereof for introducing material into avertical passage 161. The bottom end of the passage 161 is closed by anozzle 162, which includes a small diameter outlet orifice 163 and acylindrical guide 164 for the plunger 158. One side of the guide 164 isprovided with a vertical passage 165 for material dispensed by thenozzle device.

OPERATION

The apparatus of the present invention is intended for use with the shotsize selector device disclosed in applicant's copending Canadian patentapplication Ser. No. 277,382, filed May 2, 1977. The slot size selectorsensor 14 will operate in conjunction with an indicator (not shown) onthe mold carrier 2 to dispense a quantity of heel filling materialdependent upon the volume of the heel cavity. However, the shot sizeselector device does not form part of the present invention.

In order to operate effectively, it is merely necessary to provide apair of switches (not shown) for closing by the mold carrier 2 and heelof each mold 3, respectively. Since it is essential that a shot ofplastic material be dispensed at regular intervals, in the absence of amold 3, closing of the switch actuated by the mold carrier 2 only wouldresult in a purging step, i.e. a shot of thermoplastic material would bedischarged between the carrier forks into a receptacle beneath the moldconveyor.

If a mold 3 is present, both switches are closed to start a heel fillingoperation. The clutch 70 is engaged to cause the nozzle device 39 tomove in unison with the mold 3. As the injection unit 34 rotates on theplate 44 and the shaft 35, the cam device 126 causes the carriage 30with the injection unit 34, shaft 35 and plate 44 to move away from theconveyor chain 1 as the roller 140 moves to the midpoint of its path oftravel in the cam groove 138, and then towards the chain 1 as the roller140 moves past the midpoint of the cam groove 138. Thus, instead offollowing an arcuate path overlapping the straight line path of travelof each mold 3, the nozzle device 39 is caused to follow a straight linepath of travel above each mold 3. During movement of the nozzle device39 with the mold, a very low pressure may be applied to the piston rodend of the cylinder 116 to assist movement of the plate 44 and injectionunit 34.

During movement of the nozzle device 39 with the mold 3, thermoplasticmaterial is dispensed via the nozzle 162 into the heel cavity of themold 3. The degree and duration of opening of the nozzle 162 arecontrolled according to the size of the heel cavity using a timer (notshown) pre-set to match the heel size. As soon as the mold carrier 2strikes a third switch (not shown) the injection unit 34 and the nozzledevice 39 are returned to their initial positions upstream in the pathof travel of the chain 1 (to the right in FIG. 2) ready for another heelfilling operation.

With the apparatus illustrated in FIG. 1, each mold carrier 2 firstactuates the pneumatic limit switch or valve 13, which moves the shotsize selector sensor 14 into engagement with cams on each mold carrier 2to feed a signal to the shot size control indicative of the volume ofmaterial to be dispensed into the heel cavity of the mold 3. The cams oneach mold carrier 2 are pre-set in accordance with the size of the heelcavity by an operator at a location immediately following the coolingdevice 19. Then, the photosensor 16 located beneath the nozzle device 39of the injection unit 34 is occluded by the heel of the mold 3 toenergize the clutch 70 which starts movement of the injection unit 34with the mold 3.

Four switches (not shown) are located beneath the rear or outer end ofthe injection unit 34 for actuation by a magnet mounted on the bottom ofthe plate 44. The first switch indicates the rest position of theinjection unit 34. The second switch initiates heel filling, i.e. opensthe nozzle 161 and starts injection. The heel filling step is terminatedby the shot size control of the shot size sensing device. The thirdswitch acts as a safety switch to terminate injection in the event thatthe shot size control is defective, and disengages the clutch 70 topermit the injection unit 34 to return to the rest position. The fourthswitch is a safety switch override for the third switch, i.e. in theevent of malfunctioning of the third switch to effect the sameoperations as the third switch.

At the end of a heel filling operation, in order to return the injectionunit 34 and the nozzle device 39 rapidly to their initial position thecylinder 116 is actuated to swing the shaft 35, injection unit 34 andnozzle device 39 to such initial position. Rapid return of the heavyinjection unit 34 is cushioned by the shock absorber 122, which isengaged by the arm 123 on the plate 44. During return of the injectionunit 34 to the initial position, the roller 140 remains in the camgroove 138.

For manual purging or servicing, the cam follower, i.e. the roller 140is retracted from the cam groove 138 to free the plate 44, and thecylinders 124 are actuated to move the carriage 30, injection unit 34and nozzle device 39 away from the chain 1 of the molding machine.

We claim:
 1. A method of slush molding articles of footwear includingheel and upper portions comprising the steps of continuously conveying aplurality of molds along a path of travel; filling each mold with aplastisol; heating said molds to cure a portion of said plastisol,thereby forming a plastisol skin on the interior of the mold;discharging excess plastisol from the mold while leaving the skin in themold; moving a heated injection unit in synchronism with said molds froma rest position over a preselected portion of said path of travel;dispensing a preselected quantity of thermoplastic material from saidinjection unit into said heel cavity during such synchronous movement tofill the heel cavity; returning said injection unit to the restposition; and curing said heel portion.
 2. A method according to claim1, wherein said thermoplastic material is recycled, waste thermoplasticmaterial.
 3. A method according to claim 2, wherein said thermoplasticmaterial is obtained by trimming excess portions of said skin formedduring the slush molding process.